Understand Focal Length in 4 Easy Steps

Why You Should Know What Focal Length Means

Knowing what the focal length means, especially in relation to your camera, is very important when it comes to buying lenses. Read this post to find out what different lenses are used for, which ones are right for you, how to use them creatively, and all the technical speak you’ll need.

Section 1 – What Does it Actually Mean?

The focal length of your lens essentially determines how ‘zoomed in’ your photos are. The higher the number, the more zoomed your lens will be.
It is often misunderstood that the focal length is measured from the front or rear of the lens when, in reality, it’s the distance between the point of convergence in your lens to the sensor or film in your camera.
Take a look at the diagram below that explains this:

Section 2 – Different Focal Ranges and What They’re Used For

Ultra Wide Angle 14-24mm

These lenses are often considered specialty items and the range is not often included as part of a kit lens. They create such a wide angle of view that they can appear distorted as our eyes aren’t used to seeing that sort of range.
Ultra wide angle lenses are often used in event and architectural photography for getting a lot into a photo when shooting in a confined space. Wide and ultra wide lenses are about putting yourself in the middle of it all, rather than simply fitting in the whole of a scene.
These lenses are not particularly suitable for portraits as they enhance the perspective so much that facial features can look unnatural.

Wide Angle 24-35mm

This is where you’ll find most kit lenses for full frame cameras start. 24mm is roughly the point at which the distortion that appears to stretch the side of an image stops appearing unnatural.
They are used widely by photojournalists for documenting situations as they are wide enough to include a lot of the context whilst still looking realistic.

Standard 35mm-70mm

It’s in this range (at about 45-50mm) that the lens will reproduce what our eyes see (excluding peripheral vision). I personally like to use this range when shooting on the street or with friends in a close setting such as at the dinner table or the pub.
A standard lens such as a 50mm f1.8 is an excellent, inexpensive addition for a camera and will provide excellent results. Prime lenses (lenses with a fixed focal length – can’t zoom) will always provide better results than your kit lens as it is built with a single purpose in mind. It does one job well rather than multiple jobs poorly.

Mild Telephoto 70-105mm

This range is often where kit lenses stop and you’ll start to get into the range of telephoto lenses and portrait primes (around 85mm). This is a good range for portrait lenses. The natural perspective of the lens will separate the face from the background without completely isolating it.

Telephoto 105-300mm

Lenses in this range are often used for distant scenes such as buildings or mountains. They’re not suitable for landscape photography because of the way they flatten the perspective of a scene. Lenses in a range higher than this are mostly used for sport and animal photography.

Section 3 – How Does Focal Length Affect the Perspective of A Photo?

I tackled most of this in the previous section. To give you a better idea of how the focal length affects the perspective of a photo, I took four photos of the same subject at different focal lengths and compared them below.
The subjects (three soup cans) remained in the same position (about 10 inches apart from one another) in every photo. It’s worth noting that these photos are shot with a crop sensor. This means the actual focal length will be higher than listed – something I explain in Section 4.
To say it’s the focal length that changes the perspective is, however, quite misleading. You see, it’s actually the distance from the subject.
The focal length is an indicator of the distance from the subject: the images are all framed the same. Differences arise because the focal length is getting longer (zooming in) as the camera moves further away from the subject.Remember, the distance from the subject is changing the perspective. The focal length is just used to compensate for this.

Section 4 – What About My Crop Sensor?

Shooting on a crop sensor has what’s known as the ‘crop factor’. This essentially means that any full frame lenses (EF, FX, etc.) that you put onto a crop sensor body will have a cropping effect.
The crop factor is approximately 1.6. In real terms, this means that if you shoot at 35mm, the actual result will be closer to a 50mm image.
The diagrams below show the way this works. What you’re effectively doing is zooming in on an image, and avoiding the widest parts of the scene.
Even lenses built for crop cameras such as the EF-S range and DX range will still have this effect. This is because lenses are listed by their actual length rather than their field of view.
These lenses will not work on a full frame body without a heavy vignetting effect. The image will not project onto the whole of the sensor.
That’s it! Finally, here are two example shots taken at very different focal lengths. The first is shot at 24mm and the second at 300mm (both on a crop sensor).
You can learn more about the basics of focal length here.

I Need Help With…

117 comments

Hey there, first of all, thanks; no one ever explained it so well before. Im so happy to have found this website 🙂 I do have to mention, though, a wonderful website like this loses credibility with such spelling mistakes as “How does the focal length ‘effect’ the perspective of a photo?” Effect and Affect are two different words. The focal length AFFECTS the perspective, therefore it gives you a different EFFECT on the picture. Believe me, this comment goes with the best intentions, I truly love the site.
Cheers

Thanks JMM, I got a few posts in before that started to dawn on me and as it’s in a heading, it must have slipped through the net. I did have a really good editor, but she’s away at the moment. I’ll get her back on it when she’s back!
Josh

Josh, thanks so much for the info. Like the saying goes…. “A picture is worth a thousand words”!! It’s so nice to have somethings explained to where the “average” person, like me, can understand it!! I appreciate it!!

very good site josh,also easy to understand i’m new to photography,and its hard to understand a lot of the terminology,if you know nothing about it,i see you sign your photographs.how is this done i use a mac with’ i photo’ only so far . thanks

Hi Josh,
The conversations do reflect your expertise in photography.
From your responses to various queries I am quite sure you can answer mine. I tried taking some moon pics with my canon rebel xti with quantaray 70 – 300 mm lens. for some reason, the pic always seems to be very small (smaller than the ones I have seen on the net – not that thse have been taken with high end lens). Request your guidance and thanks in advance. Cheers… Sanjay.

Do you mean the actual moon looks really small? It’s funny you should mention it because my friend came over last night with a photo of a moon on his camera taken with his brand new 70-300 at it was also small. The moon is far too far away to capture at a good size, even at 300mm. Professionals will likely have used longer focal lengths and 2X entenders which double the focal length. What I recommend you do is work on your exposure so that you can see detail on the moon and wait for a night where the moon is particularly large. Then shoot at your maximum resolution and crop the image around the moon for the best effect. Hope this helps – Josh

Wow! Blown away here! Fantastic how you put this article together.
I have to ask, how does the “submit a photo” thing work, maybe an article on THIS?
I don’t know how I found this site but I’m glad I did. For sure, I will return often.
I’ve added this to my INFAMOUS Pearl Tree. You sir are now a rock star.
Keep up the good work and Psss.. “You’re a Pro” You can’t fool me.

Great article, Josh! I have been struggling with this subject for a while. You cleared it up in a few paragraphs. Wonderful talent, that!
I’m a little slow, I guess (well, I know, but I like to hide it some), but I miss the correlation between the last example photos. I was hoping to see a comparison of the two extremes on the same subject, so I may be missing the point entirely.

Perhaps they’re not great examples, but if you look at the trees in the first one, they’re far apart and you can see the details between them, where as the plants in the second one are much more pushed together, so that you can’t really get a sense of depth. I might consider changing them at some point, thanks, Josh

Josh, I did not mean to knock the examples, but just to indicate that I missed the point of comparison. Trust me, I am far too ignorant of photography to believe that I could critique anything! Just trying to learn.
Thanks for the clarification!

I wonder this article with so stupid mistakes is widely reposted. I wonder all photographers didn’t learn optics in school and cann’t just read wiki. At first, focal lenth is not the distance to the sensor (but to the image of infinitely distant object). Just try to unplug your lens – FL wouldn’t become several meters. At second, the lins at the picture looks like having focus inside it, named “the point of convergence”. Beginner will hardly understand the reality.

Hello and Merry Christmas
Thanks for the article; looking around and noticing the quality of your posts it becomes clear that I will spend a lot of time on your site.
I do have a questions though. I’m a beginner and putting together an equipment list. As far as the camera is concerned I decided on Nikon D5300. It is still unclear to me what to pick as prime lens for this camera body. I was thinking to get the AF-S NIKKOR 50mm f/1.8G. My confusion is in regards to the focal length. Since this camera has a 1.5 crop sensor, should I get the AF-S DX NIKKOR 35mm f/1.8G instead?
Thank you

Shooting on a crop sensor has what’s known as the ‘crop factor’. This
essentially means that any full frame lenses (EF, FX, etc.) that you put onto a crop sensor body will have a cropping effect.
The crop factor is approximately 1.6. In real terms, this means that if you shoot at 35mm, the actual result will be closer to a 50mm image.

This is in correct, at least in part. I put a 35mm Takumar lens (FX, m42-mount) onto a K&F m42-m4/3 glass-less adapter (no lenses inside, just a metal tube) and this onto my Olympus E-M5 MarkII micro-four-thirds camera, and the field of view was not the same as when using a native 17mm* lens on that camera (no adapter needed). The field of view with the 35mm FX lens was the same as a native, m4/3 35mm lens (I used my kit lens zoomed to 35mm).
APS cameras have a 1.5X crop factor; m4/3 cameras have a 2X crop factor.